[segyio] 332/376: Add negative indexing on segy.header

[Jørgen Kvalsvik]

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jokva-guest pushed a commit to branch debian
in repository segyio.

commit 58dd5f03ef4c390700f1c04cc1fcf88e455eda48
Author: Jørgen Kvalsvik <jokva at statoil.com>
Date:   Fri Aug 11 10:02:33 2017 +0200

    Add negative indexing on segy.header
---
 python/segyio/_field.py | 7 +++++--
 python/test/segy.py     | 9 +++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/python/segyio/_field.py b/python/segyio/_field.py
index 0024b13..02ac76f 100644
--- a/python/segyio/_field.py
+++ b/python/segyio/_field.py
@@ -90,8 +90,11 @@ class Field(object):
 
     @classmethod
     def trace(cls, buf, traceno, segy):
-        if traceno >= segy.tracecount:
-            raise IndexError("Trace number out of range: 0 <= %d < %d" % (traceno, segy.tracecount))
+        if traceno < 0:
+            traceno = segy.tracecount + traceno
+
+        if traceno >= segy.tracecount or traceno < 0:
+            raise IndexError("Header out of range: 0 <= %d < %d" % (traceno, segy.tracecount))
 
         if buf is None:
             buf = segyio._segyio.empty_traceheader()
diff --git a/python/test/segy.py b/python/test/segy.py
index 5bc7220..35b6a1e 100644
--- a/python/test/segy.py
+++ b/python/test/segy.py
@@ -471,6 +471,15 @@ class TestSegy(TestCase):
             self.assertEqual(1, f.header[0][189])
             self.assertEqual(1, f.header[1][TraceField.INLINE_3D])
             self.assertEqual(1, f.header[1][segyio.su.iline])
+            self.assertEqual(5, f.header[-1][segyio.su.iline])
+            self.assertEqual(5, f.header[24][segyio.su.iline])
+            self.assertEqual(dict(f.header[-1]), dict(f.header[24]))
+
+            with self.assertRaises(IndexError):
+                f.header[30]
+
+            with self.assertRaises(IndexError):
+                f.header[-30]
 
             with self.assertRaises(IndexError):
                 f.header[0][188] # between byte offsets

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